| Summary: | 碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 104 === Photochromic molecules are widely applied in chemistry, physics, biology, and materials science. Despite lots of photochromic systems have been developed, their applications are still limited regarding they generally involved complicated synthesis procedures, and the low fatigue resistance, or incomplete light conversion. Rhodamine is a class of dyes with excellent optical properties including long-wavelength absorption, large absorption coefficient, and high photostability in its ring-open form. In this work, rhodamine acetohydrazide (RdaH) metal complex was found to undergo intramolecular ring-open reactions upon UV irradiation, leading to fluorescence change in solution. Interestingly, the tin-chelated complex exhibited an extremely long lifetime in the photo-induced excited state. The activation energy of the complexes chelated to different metal ions was therefore accessed. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were also obtained through the use of cyclovoltammetry (CV). It was proposed that UV light promoted metal ligand charge transfer (MLCT) from the rhodamine moiety to metal ion, which considerably promoted the emission of the rhodamine moiety.
In addition, polypeptide containing a rhodamine center was also synthesized in this study. A rhodamine hydrazide (RdH) was served served as initiator to proceed ring-opening polymerization (ROP) of cyclic monomer to result in poly(γ-propargyl-L-glutamate) (PPLG) chain containing fluorescent Rd center. With the spirolactam ring, the RdH initiator is non-fluorescent but during the course of ROP the cyclic monomer acted as proton-transfer agent to catalyze the opening of the spirolactam ring of RdH, thus generating PPLG polypeptide containing an fluorescent rhodamine center. The rhodamine center of PPLG exhibits the novel aggregation-induced emission (AIE) behavior according to its solution emission response toward concentration and aggregation. Two PPLGs with low and high MWs were prepared and characterized to evaluate the influence of secondary structures of peptide chains on the resolved AIE-related emission behavior. Also, the PPLGs were found to complex with metal ions, rendering complexes with the MLCT property. Upon UV irradiation, the PPLG metal complex undergoes distinct color and fluorescence change. A similar reversible photochromism was also identified in PPLG metal complex.
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